Communication systems in general and paging systems in particular using selective call signalling have attained widespread use for calling a selected paging system receiver by transmitting information from a base station transmitter to the paging receiver. These small, compact paging receivers are extensively used in many different places and applications. In some places, such as movie theaters or the like, it is beneficial to provide a silent signal by generating an alert with mechanical vibrations instead of alert tones.
Numerous prior art paging receivers have developed vibration motion in the paging receiver by attaching an eccentric mass to a shaft being rotated by an electric motor. Examples of these prior art paging receivers are U.S. Pat. Nos. 3,623,064 and 3,911,416. These prior art vibrator alerting devices which require an eccentric mass to be mechanically attached to the shaft of the electric motor.
Numerous problems have been discovered by the Applicant in these prior art paging receivers. For example, since the eccentric mass is coupled to the shaft of the electric motor, the vibration motion of the mass is transmitted to the paging receiver housing through the electric motor casing. The vibratinn motion is transmitted to the housing through the bearings of the motor shaft. This has a tendency to quickly wear out the bearings of the shaft, causing excessive noise of the motor in operation and eventually causing the failure of the electric motor.
Another disadvantage is the shock load transmitted by the mass to the shaft when the paging receiver is mishandled or dropped. A strong enough shock can result in deforming the shaft and permanently damaging the motor.
Another problem of the prior art vibrator alerting devices is the vibration motion, generated by the eccentric mass, is absorbed by the motor, motor case, and bearings of the shaft, causing a decrease in the vibration sensation of the paging receiver.
These problems have caused manufacturers to purchase motors having very expensive bearings which increases the cost of the paging receiver to the consumer. Ultimately the resulting failure of the electric motor requires the consumer to replace the electric motor.